The invention relates to a device for the closure of a vessel and/or forming and pressing semi-finished products by means of a rotation-symmetric reciprocating piston mechanism of extremely compact design, which includes a hydraulic piston and an intensifier piston, each of which run in cylinders. The hydraulic piston is driven using water, the intensifier piston pneumatically, the two forming a direct axial functional unit via a fluid located in a space between the lower face of the hydraulic cylinder and the upper face of the intensifier piston. The upper face of the hydraulic piston forms at least partially the closure part of the vessel or it is rigidly connected to a closure element for the vessel, or the upper side of the hydraulic piston forms the tools or is rigidly connected to said tools.
The spectre of products developed by the semiconductor manufacturing, opto-electronic and other industries is constantly expanding and the said products permit to realise the central functions with the aid or on the basis of micro or nano-structures. The said structures also react extremely sensitive to minor impurities during the production phase. Hence, ever more stringent requirements are specified for the admissible emission rates of components used in the said ambience. The cleaning steps required for nano-structured surfaces cannot be carried out by conventional cleaning agents or they are hardly feasible. For some time supercritical fluids have been used on a large scale as they enhance the wetting effects and cleaning results. These operations necessitate process pressures which range from 150 to more than 300 bars and which consequently require special equipment. So far high-pressure equipment with adequate mechanical properties was not directly suitable for clean room operations or it was even unsuitable for such applications. This invention describes a high-pressure unit of a very compact design which is suited for clean-room applications at high pressure levels and which only produces minor emissions when alternating load cycles take place at high pressure level.
Reciprocating piston mechanisms for pressures of >150 bar are in broad and diverse technical and commercial use and have been adequately described in patent-specific and general technical literature.
Reciprocating piston mechanisms which include, inter alia, hydraulic pistons and intensifier pistons, with the upper face of the intensifier piston acting axially on an operating fluid, which is enclosed in the cylinder chamber below the lower face of the hydraulic piston and causes the working stroke or maximum pressure on the hydraulic piston, are also known from the relevant literature.
Specifications DE 100 26 616 A1 and WO 01/69088 A1 describe the above-mentioned reciprocating piston mechanisms in which the operating fluid of the hydraulic piston and that of the pressure intensifier is identical. JP 55126103 discloses such a reciprocating piston mechanism, which is equipped with an additional vessel in which displaced hydraulic fluid is temporarily stored. WO 01/69088 A1 also describes a return function of the hydraulic piston, the function being executed in such a way that the plunger of the hydraulic piston travels in a spring, which is clamped in the course of the piston stroke between the cylinder head and the bottom of the piston. The spring relaxes and returns the hydraulic piston to its initial position when the action of force on the piston ceases.
Also known from and adequately described in the relevant literature are reciprocating piston mechanisms which include for the hydraulic piston an operating fluid different to the operating fluid for the intensifier piston. The hydropneumatic devices described in Specifications JP 09280202 and DE 199 46 678 A1 may be mentioned here as examples of such combined mechanisms.
Liquids and gases are used as the operating fluids, mainly water being used for pressures of up to around 160 bar, and hydraulic fluids above 160 bar. Inert gases and air are the most commonly used gaseous operating fluids. Hydraulic fluid exhibits important beneficial characteristics in terms, inter alia, of lubrication of sliding surfaces, low compressibility and high temperature stability.
Detrimental effects which cannot be completely eliminated from piston-based devices include, inter alia, material erosion and operating fluid leakage. Friction- and pressure-induced material erosion, such as abrasion, evaporation and liquefaction, for example, occur to a limited extent even on the parent material itself and, in particular, in and on the sealing system. Material erosion in reciprocating piston mechanisms is a function essentially of the surface quality of the sliding surfaces and the manufacturing tolerances of the components, of the sealing material and the radial contact pressure of the sealing member, and also of temperature.
Leakage of the operating fluid, certain quantities of which are entrained at every piston stroke, is functionally dependent on, inter alia, quality of surfaces, viscosity, hydrostatic pressure in the cylinder chamber and also on the sealing system and sealing member design and the radial contact pressure of the sealing members and sealing system.
High working pressures necessitate adequate lubrication of the surfaces facing each other and running against one another, resulting in corresponding leakage quantities. This effect can be minimized by means of suitable sealing systems and a high-quality surface treatment. The potentials for increasing contact pressure in order to suppress leakage are however restricted by the fact that the degradation and erosion of the sealing material increases as pressure rises, with the consequences of emissions and, subsequently, greater leakage quantities. In addition, the limits of mechanical load-bearing capacity and economic operation are reached.
Impurities resulting from material erosion and leakage from the above-mentioned sources are of extreme disadvantage in the production zone, particularly in the case of cleanroom processes. Clean-room classes are defined, for example, in DIN 2083 and Federal Standard 209D. Emissions of any type whatsoever have a direct influence on the quality of the products of these processes and a high level of equipment and organizational input is applied to minimize such emissions, inevitably with high associated costs. Of particular seriousness and disadvantage is contamination with oil mists, since oil-containing emissions are in many cases chemically active and can be removed again only using solvent-containing agents which, for their part, are not desirable in cleanrooms and can, indeed, be extremely disadvantageous there.
It is known that fluid-hydraulic reciprocating piston mechanisms used in cleanrooms are somewhat problematic and have to be rendered suitable for cleanroom applications by means of appropriate exhausting systems (SWISS Contamination Control 5 (1992) No. 5, p. 8 ff.). Oil depositions occurred on the semi-finished product when a pressing die was used for the production of CD blanks, for example. Investigations revealed that the hydraulic fluid was the source of this impurities. The necessary suitability for cleanroom use was restored by fitting sealed sleeves to the die's connecting rods and by means of exhausting of the press housing and of the air from the sleeves.
A further technical article discloses a pneumatic cylinder with no piston-rod (Dr.-Ing. E. Fritz; Paper for the 1st Int. Forum Fluidtechnisches Kolloquium, Volume 2, pp. 283 ff.). Suitability for cleanroom service was achieved by generating a partial vacuum in the space between the covering strip and the sealing strip. Vacuum connections were fitted to the cylinder tube for this purpose, and the emissions were routed away.
A disadvantage of the above-mentioned reciprocating piston mechanisms incorporating an exhausting system is the fact that additional systems are necessary for the assurance of minimum particle concentrations and that these systems must be installed and continuously operated.
Spatial separation is implemented in the case of more complex production systems, in which components with cleanroom capability are used simultaneously with less suitable components. The equipment not suitable for cleanroom service is accommodated in so-called “maintenance zones”, while the cleanroom-capable equipment is housed in so-called “white rooms”. Such solutions necessitate complex and expensive fluid-lock systems and organizational precautions in order to ensure the exclusion of impurities from the “maintenance zone”.
U.S. Pat. No. 6,067,728 disclosed a device and a process for the drying of wafers using supercritical CO2, a pneumatico-mechanical closure device being incorporated. The closure of the vessel plug is accomplished by means of a pneumatic piston and lever device, pre-pressurization being achieved by means of this arrangement. The plug is locked in place by means of clips. After pneumatico-mechanical closure of the process room, one or more static clips are positioned symmetrically on the edge of the cover. These closure clips are pushed mechanically over the edge of the vessel leakage and the vessel base and provide the tightness of the vessel during the process, as internal pressure rises.
A disadvantage of the above-mentioned invention are the many moving parts, which may be regarded as critical in terms of emissions, and which severely limit the number of reciprocating strokes and/or number of possible process cycles per unit of time, as a result of the necessary movements. In addition, the many operations required also necessitate a complex control device.